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27 Feb 2006

Volume 88, Issue 9, Articles (09xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 88, 093101 (2006); http://dx.doi.org/10.1063/1.2179133 (3 pages)

C. X. Xu, X. W. Sun, Z. L. Dong, G. P. Zhu, and Y. P. Cui
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Suppression of crack generation in GaN epitaxy on Si using cubic SiC as intermediate layers

Jun Komiyama, Yoshihisa Abe, Shunichi Suzuki, and Hideo Nakanishi

Appl. Phys. Lett. 88, 091901 (2006); http://dx.doi.org/10.1063/1.2175498 (3 pages) | Cited 20 times

Online Publication Date: 27 February 2006

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We demonstrate suppression of crack generation in GaN epitaxy on Si using cubic SiC as intermediate layers. Crack-free GaN with a thickness of 2 μm was obtained. Epilayers of SiC (0–1 μm), thin AlN (50 nm), and GaN (1–3 μm) were prepared on 3 in. (1 1 1) Si substrates (GaN/AlN/SiC/Si) by metalorganic vapor-phase epitaxy. Cracking of GaN is suppressed with thicker SiC (1 μm), whereas cracks are generated in GaN without SiC and with thinner SiC (50 nm). Transmission electron microscopy analysis revealed monocrystalline wurzite structure of GaN. Current-voltage measurements showed breakdown voltage exceeding 250 V, indicating its potential for high voltage application.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
68.55.-a Thin film structure and morphology
73.61.Ey III-V semiconductors
68.60.Bs Mechanical and acoustical properties
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Infrared fluorescence and optical gain characteristics of chalcogenide-bound erbium cluster-fluoropolymer nanocomposites

G. A. Kumar, R. E. Riman, S. Banerjee, A. Kornienko, J. G. Brennan, S. Chen, D. Smith, and J. Ballato

Appl. Phys. Lett. 88, 091902 (2006); http://dx.doi.org/10.1063/1.2170433 (3 pages) | Cited 7 times

Online Publication Date: 27 February 2006

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The infrared fluorescence and optical gain characteristics of optically transparent nanocomposites consisting of (THF)14Er10S6Se12I6 (“Er10”) or (DME)2Er(SC6F5)3 (“Er1”) clusters dissolved in a transparent hexafluoroisopropyl (6F) variant of a perfluorocyclobutyl (PFCB)-based fluoropolymer are reported. Under excitation at 980 nm, fluorescence was observed at 1540 nm from both Er10 and Er1 with a 3dB bandwidth of 96 and 60 nm, respectively. The maximum gain computed for Er10 and Er1 was 2.8 and 0.021 dB/cm, respectively. The corresponding threshold pump powers for Er10 and Er1 were calculated to be 1.7 and 0.2 mW, respectively. These computations are consistent with gain characteristics measured by the amplified spontaneous emission technique and suggest that these nanocomposites are promising materials for active optical devices.
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78.55.Kz Solid organic materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
42.70.Jk Polymers and organics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.45.+h Stimulated emission

Lowering critical cooling rate for forming bulk metallic glass

T. D. Shen and R. B. Schwarz

Appl. Phys. Lett. 88, 091903 (2006); http://dx.doi.org/10.1063/1.2172160 (3 pages) | Cited 7 times

Online Publication Date: 27 February 2006

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Small volumes of Pd44Ni10Cu26P20 and Pd43.2Ni8.8Cu28P20 were encapsulated in B2O3 and thermally cycled between Tg−60 °C and Tl+60 °C, where Tg and Tl denote the alloys’ glass transition and liquidus temperatures. After this thermal treatment, the critical cooling rates (CCRs) for glass formation can be lowered by an order of magnitude, resulting in a critical cooling rate significantly lower than that reported for any other glass forming alloy melt. These experiments demonstrate that the CCR is not constant but strongly dependent on the degree of heterogeneous nucleation.
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81.05.Kf Glasses (including metallic glasses)
81.05.Bx Metals, semimetals, and alloys
61.43.Fs Glasses
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
81.40.Gh Other heat and thermomechanical treatments

Quantifying stoichiometry of mixed-cation-anion III-V semiconductor interfaces at atomic resolution

K. Mahalingam, K. G. Eyink, G. J. Brown, D. L. Dorsey, C. F. Kisielowski, and A. Thust

Appl. Phys. Lett. 88, 091904 (2006); http://dx.doi.org/10.1063/1.2178771 (3 pages) | Cited 3 times

Online Publication Date: 27 February 2006

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Employing the focal-series reconstruction technique in high-resolution transmission electron microscopy, we obtained true atomic resolution images of interfacial disorder within cation and anion sublattices across interfaces in an InGaSb/InAs heterostructure. This enabled independent quantitative mapping of changes in the In–Ga and As–Sb contents across interfacial regions ∼ 0.6 nm in width. A comparison of the cation and anion sublattice images revealed that intermixing at the InGaSb‐on‐InAs interface is confined to the In–Ga sublattice. Also, atomic scale roughness within the As–Sb sublattice of the InAs‐on‐InGaSb interface was discerned. This approach is general, permitting atomic-scale compositional analysis of heterointerfaces with two species per sublattice.
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68.35.Ct Interface structure and roughness
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation

Equation of state for fluid helium-3 based on Debye phonon model

Y. H. Huang, G. B. Chen, and V. D. Arp

Appl. Phys. Lett. 88, 091905 (2006); http://dx.doi.org/10.1063/1.2178867 (3 pages) | Cited 1 time

Online Publication Date: 27 February 2006

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An equation of state for math using the Helmholtz potential function has been developed. It is based on the Debye phonon model which goes smoothly to zero in the limit of zero temperature, and reduces to the ideal gas in the limit of zero density and/or very high temperature. The lower temperature limit of the equation 10 mK is safely above the superfluid transition at 2.6 mK. The upper limit of 60 K is approximately the upper limit of available math properties measurements. The certain pressure range of validity of the equation is from about 0 to the melting pressure or 15 MPa. State properties are determined from the Helmholtz energy by standard thermodynamics.
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67.30.H- Superfluid phase of 3He
64.30.-t Equations of state of specific substances
65.40.G- Other thermodynamical quantities

Quantification of the meniscus effect in adhesion force measurements

J. Grobelny, N. Pradeep, D.-I. Kim, and Z. C. Ying

Appl. Phys. Lett. 88, 091906 (2006); http://dx.doi.org/10.1063/1.2181200 (3 pages) | Cited 22 times

Online Publication Date: 28 February 2006

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Adhesion forces between a gold sphere and flat gold substrate are studied using atomic force microscopy in different environments. The pull-off force measured in a vacuum is found to be a small fraction of that in ambient air or nitrogen atmosphere. Calculations of capillary condensation forces, including the effects of elastic deformation of the contacting bodies and of adsorption layers, reveal that the meniscus force is the dominant source of the observed difference in pull-off forces. The experimental data show that nitrogen purge does not eliminate the meniscus contribution to the pull-off force.
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68.35.Np Adhesion
68.43.Mn Adsorption kinetics

Cusp instability and phase field in forced velocity solidification of binary alloys

J. S. Kirkaldy

Appl. Phys. Lett. 88, 091907 (2006); http://dx.doi.org/10.1063/1.2179146 (3 pages)

Online Publication Date: 1 March 2006

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Current phase field processing of our cuspoidal wavelength data by Greenwood et al. [ M. Greenwood, M. Haataja, and N. Provatas, Phys. Rev. Lett. 93, 246101 (2004) ] exhibits a qualitative positive comparison with the calibrated optimal codes for wavelengths in the intermediate and high velocity zones, but a shortfall for the near-marginal zone, and does not attempt to deal with wave amplitudes. The successful steady state theories as herein expanded to the near-marginal zone and to wave amplitudes offer a further predictive challenge to the asymptotic and potentially more comprehensive time-dependent phase field paradigm.
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81.30.Fb Solidification
64.70.D- Solid-liquid transitions

Indentation size effect in barium titanate with spherical tipped nanoindenters

T. Scholz, J. Muñoz-Saldaña, M. V. Swain, and G. A. Schneider

Appl. Phys. Lett. 88, 091908 (2006); http://dx.doi.org/10.1063/1.2177364 (3 pages) | Cited 11 times

Online Publication Date: 1 March 2006

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Nanoindentation tests in an 90°-ac-domain area of an {001} orientated barium titanate single crystal were performed using four different indenters (two with cube corner and two with spherical shape) with tip radii from 61 nm to 1.9 μm. Extensive calibrations of the tips on fused quartz and sapphire defined the penetration depth range for approximately spherical contact prior to indentation of barium titanate (BaTiO3). The measured elastic modulus is independent of the different indenters. The measurements showed plastic deformation after “pop-in”. The calculated mean pressure remained constant for each indenter, but clearly depends upon the indenter radius. The indenter radius dependence of the hardness support the concept of “geometrically necessary dislocations”, proposed by W. D. Nix and H. Gao [J. Mech. Phys. Sol., 46, 411 (1998)] and its extension to spherical tipped indenters [J. G. Swadener, E. P. George, G. M. Pharr, J. Mech. Phys. Solids, 50, 681 (2002)]. The results show this concept fits the data generated with indenter radii which are at least an order of magnitude lower than investigated by Swadener. Furthermore, the results agree with estimates of the statistically stored dislocation density determined for BaTiO3.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.Qp Friction, tribology, and hardness
62.20.M- Structural failure of materials
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
81.40.Lm Deformation, plasticity, and creep

First-principles study of the (001) surface of cubic BaZrO3 and BaTiO3

Yuan Xu Wang, Masao Arai, Taizo Sasaki, and Chun Lei Wang

Appl. Phys. Lett. 88, 091909 (2006); http://dx.doi.org/10.1063/1.2178416 (3 pages) | Cited 10 times

Online Publication Date: 1 March 2006

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First-principles density functional calculations are employed to study the (001) surface of BaZrO3 with both BaO and ZrO2 termination. Surface structure and band structure have been obtained. For the ZrO2-terminated surface, the large displacement of the O atoms in the first layer results in the small surface rumpling. In addition, the largest relaxation appears on the second layer atoms but not on the very first layer ones. The analysis of the structure relaxation parameters reveals that the rumpling of the (001) surface for BaZrO3 with the BaO termination is stronger than that of BaTiO3. The origin of the different surface relaxation behavior between the two materials is discussed. The surface state appears in the band structure of the ZrO2-terminated surface of BaZrO3.
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68.47.Gh Oxide surfaces
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
73.20.At Surface states, band structure, electron density of states

In situ photoelectron emission microscopy of a thermally induced martensitic transformation in a CuZnAl shape memory alloy

Gang Xiong, Alan G. Joly, Kenneth M. Beck, Wayne P. Hess, Mingdong Cai, Stephen C. Langford, and J. Thomas Dickinson

Appl. Phys. Lett. 88, 091910 (2006); http://dx.doi.org/10.1063/1.2177450 (3 pages) | Cited 7 times

Online Publication Date: 1 March 2006

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We report photoelectron emission microscope observations of the thermal martensitic transformation in a CuZnAl shape memory alloy. The phase transformation appears at 48 °C during heating and at 42 °C upon cooling. The transformation is marked by a sharp change in photoelectron intensity, as well as a significant displacement and reorientation of surface features. The difference in the photoelectron intensity before and after the transformation is attributed to a change in work function of about 0.2 eV. Photoemission electron microscopy provides real-time information on microstructural changes and phase-dependent electronic properties.
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81.30.Kf Martensitic transformations
68.37.Xy Scanning Auger microscopy, photoelectron microscopy
64.70.K- Solid-solid transitions
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
81.40.Gh Other heat and thermomechanical treatments

Growth mechanisms of thin-film columnar structures in zinc oxide on p-type silicon substrates

J. W. Shin, J. Y. Lee, T. W. Kim, Y. S. No, W. J. Cho, and W. K. Choi

Appl. Phys. Lett. 88, 091911 (2006); http://dx.doi.org/10.1063/1.2174829 (3 pages) | Cited 9 times

Online Publication Date: 1 March 2006

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X-ray diffraction analysis reveals that the crystallinity of (0001)-oriented columnar grains in ZnO thin films grown on p-Si (100) substrates is enhanced with increasing growth temperature, and transmission electron microscopy confirms that the columnar structures become more stable at higher growth temperature. The morphological evolution of the columnar structure in ZnO thin films is described on the basis of experimental measurements.
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81.05.Dz II-VI semiconductors
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.Cd Deposition by sputtering

Hydrogen-vacancy related defect in chemical vapor deposition homoepitaxial diamond films studied by electron paramagnetic resonance and cathodoluminescence

N. Mizuochi, H. Watanabe, H. Okushi, S. Yamasaki, J. Niitsuma, and T. Sekiguchi

Appl. Phys. Lett. 88, 091912 (2006); http://dx.doi.org/10.1063/1.2176860 (3 pages) | Cited 4 times

Online Publication Date: 2 March 2006

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Hydrogen-vacancy related defect (H1′) in chemical vapor deposition homoepitaxial diamond films has been investigated by electron paramagnetic resonance and cathodoluminescence. It is found that the concentration of H1′ significantly decreases as the dilution (CH4/H2) ratio decreases. It is also confirmed that the intensity of free-exciton emission (Iex) increases as the CH4/H2 ratio decreases. The complementary relationship between Iex and H1′ can be explained by considering that H1′ acts as a nonradiative recombination center which reduces the lifetime of free exciton and Iex. The suppression mechanism of H1′ is discussed by considering the balance between the growth rate and the annihilation rate of H1′ in the subsurface region.
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78.60.Hk Cathodoluminescence, ionoluminescence
76.30.Mi Color centers and other defects
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.35.-y Excitons and related phenomena
78.66.Db Elemental semiconductors and insulators
61.72.J- Point defects and defect clusters
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Microparticle manipulation using inertial forces

Michael Eglin, Mark A. Eriksson, and Robert W. Carpick

Appl. Phys. Lett. 88, 091913 (2006); http://dx.doi.org/10.1063/1.2172401 (3 pages) | Cited 4 times

Online Publication Date: 2 March 2006

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We demonstrate controlled manipulation of large quantities of microparticles on a surface using inertial forces. Motion is induced by applying a periodic parabolic wave form to a shear-polarized piezoelectric plate coupled to a substrate on which the particles reside. Particles move in steps of 10 to 50 nm per cycle, and the particle motion is mass selective. Particle velocity is varied by changing the frequency of the wave form. Calculated inertial forces acting on the particles correspond closely to friction forces between individual microparticles and the substrate, as measured by coupling an individual particle to an atomic force microscope. The results provide insight into the characteristics of particle-surface interactions, and demonstrate the potential for controlled manipulation and separation of large collections of particles without the need for a fluid medium.
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81.16.Ta Atom manipulation

Size-dependent interface energy

G. Ouyang, L. H. Liang, C. X. Wang, and G. W. Yang

Appl. Phys. Lett. 88, 091914 (2006); http://dx.doi.org/10.1063/1.2172396 (3 pages) | Cited 15 times

Online Publication Date: 2 March 2006

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A universal and analytic thermodynamic model without any adjustable parameters was established to elucidate the interface energy of multilayers at the nanometer scale by taken the size effect, the interfacial orientation, and the interfacial mismatch into account. Theoretical predictions were consistent with the calculations of the modified analytical embedded atom method and the experimental data, implying that the proposed thermodynamic model could be expected to be a general approach on nanoscale to understand interface energy in binary systems.
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68.35.Md Surface thermodynamics, surface energies
68.65.Ac Multilayers

Atomistic simulation of helium-defect interaction in alpha-iron

L. Yang, X. T. Zu, H. Y. Xiao, F. Gao, H. L. Heinisch, R. J. Kurtz, and K. Z. Liu

Appl. Phys. Lett. 88, 091915 (2006); http://dx.doi.org/10.1063/1.2178767 (3 pages) | Cited 18 times

Online Publication Date: 2 March 2006

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Molecular dynamics (MD) methods are utilized to study the formation of vacancy clusters created by displacement cascades in α‐Fe containing different concentrations of substitutional He atoms. Primary knock-on atom energies, Ep, from 500 eV to 20 keV are considered at a temperature of 100 K, and the results are compared with those performed in pure α‐Fe. There are distinct differences in the number and size of vacancy clusters within displacement cascades with and without substitutional helium atoms. It is found that many large vacancy clusters can be formed within cascade cores in α‐Fe with helium atoms, in contrast to a few small vacancy clusters observed in pure α‐Fe. The number and size of helium/vacancy clusters generally increase with increasing helium concentration and PKA energy. One of the striking results is that the number of self-interstitial atoms (SIAs) and the size of interstitial clusters are much smaller than those in pure α‐Fe.
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61.72.Yx Interaction between different crystal defects; gettering effect
61.72.J- Point defects and defect clusters

Microfabrication of millimeter wave vacuum electron devices by two-step deep-etch x-ray lithography

Young-Min Shin, Jin-Kyu So, Seong-Tae Han, Kyu-Ha Jang, Gun-Sik Park, Jong-Hyun Kim, and Suk-Sang Chang

Appl. Phys. Lett. 88, 091916 (2006); http://dx.doi.org/10.1063/1.2178770 (3 pages) | Cited 15 times

Online Publication Date: 2 March 2006

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The circuits for millimeter wave vacuum electron devices with all circuit elements including an electron beam tunnel are microfabricated by two-step deep-etch x-ray lithography (x-ray LIGA). The discrepancies of eigenfrequency between experiment and simulation are within 1.1% in a coupled-cavity structure and 1.4% in a folded waveguide structure when the operating frequency is about 100 GHz. Furthermore, a measured tolerance of below 2 μm, and a measured surface roughness of 20–70 nm, of LIGA-fabricated circuits implies the two-step LIGA microfabrication has potential applications up to the submillimeter wave region.
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81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer
85.45.Bz Vacuum microelectronic device characterization, design, and modeling

Site-selectivity of 3d metal cation dopants and dielectric response in calcium copper titanate

Sung-Yoon Chung, Si-Young Choi, Takahisa Yamamoto, Yuichi Ikuhara, and Suk-Joong L. Kang

Appl. Phys. Lett. 88, 091917 (2006); http://dx.doi.org/10.1063/1.2179110 (3 pages) | Cited 19 times

Online Publication Date: 2 March 2006

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By doping a few atomic percent of 3d-block cations, we demonstrate that the high dielectric response in CaCu3Ti4O12 can be reduced by a factor of ∼ 103 at room temperature. Each of the added dopants shows its own preferential substitution on either Cu or Ti sites. The dopants that act as acceptors have a critical impact on the disappearance of the electrostatic potential barrier at grain boundaries, resulting in drastically decreased permittivity values of <90 without voltage dependence. The present doping experiment directly shows that the potential barrier at internal interfaces is a key factor for the peculiar dielectric phenomena.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ch Permittivity (dielectric function)
61.72.S- Impurities in crystals
61.72.Mm Grain and twin boundaries

Influence of grain boundaries on the glass-transition behavior in C60 films

Jian Wu, Min Gu, Peng Bao, Duan Feng, Tong Bor Tang, and Senzu Yang

Appl. Phys. Lett. 88, 091918 (2006); http://dx.doi.org/10.1063/1.2179123 (3 pages) | Cited 2 times

Online Publication Date: 3 March 2006

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Two batches of C60 films were prepared via sublimation on Ag (111) at two different growth rates. X-ray diffraction revealed in them a preferential (111) orientation and substantial stacking faults. Their dielectric spectra at various temperatures between 80 and 300 K showed broad and asymmetric loss peaks attributable to some orientational glass transition. The nominal activation energies evaluated for the two batches are 344 and 305 meV, respectively, larger than the value of 280 meV for bulk C60. Applying Ngai’s correlated-state model, we determine the real activation energy, which then agrees well with the bulk value. We propose that, under the ac field, molecular volume changes accompany orientational “jumps” and cause local alternating stresses at grain boundaries, which correlate with the dipole reorientations. This correlation explains the deviation from Debye relaxation behavior and the increase in apparent activation energy.
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64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
61.72.Mm Grain and twin boundaries
61.48.-c Structure of fullerenes and related hollow and planar molecular structures
81.05.ub Fullerenes and related materials
68.55.-a Thin film structure and morphology
61.72.Nn Stacking faults and other planar or extended defects

Calculation of deep carrier traps in a divacancy in germanium crystals

J. Coutinho, V. J. B. Torres, R. Jones, A. Carvalho, S. Öberg, and P. R. Briddon

Appl. Phys. Lett. 88, 091919 (2006); http://dx.doi.org/10.1063/1.2181202 (3 pages) | Cited 11 times

Online Publication Date: 3 March 2006

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We present an ab initio density functional study on the electronic structure and electrical properties of divacancies in Ge. Although suffering essentially different Jahn-Teller distortions when compared to the analogous defect in Si, the relative location of the electrical levels in the gap does not differ radically in both materials. We propose a V2 model that is responsible for a donor level at Ev+0.03 eV, a first acceptor state at Ev+0.3 eV, and a second acceptor level at Ec−0.4 eV. The latter is only 0.1 eV deeper than an electron trap that has been recently linked to a divacancy in proton implanted material.
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71.55.Cn Elemental semiconductors
61.72.J- Point defects and defect clusters
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Unambiguous observation of electronic couplings between InGaAs/InGaAsP quantum dots emitting at 1.5 μm

Y. D. Jang, E. G. Lee, J. S. Yim, D. Lee, W. G. Jeong, S. H. Pyun, and J. W. Jang

Appl. Phys. Lett. 88, 091920 (2006); http://dx.doi.org/10.1063/1.2181630 (3 pages) | Cited 4 times

Online Publication Date: 3 March 2006

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We have unambiguously estimated the vertical and lateral electronic couplings between quantum dots (QDs) by comparing the carrier lifetimes at different energy positions inside the ground state band. InGaAs/InGaAsP QDs on InP(100) substrate give photoluminescence around 1.55 μm and have the dot density over 1011/cm2. The measured carrier lifetimes are almost the same across the entire photoluminescence band, indicating negligible lateral electronic coupling between QDs at this high dot density. However, for a QD sample with the 15 nm barrier spacing between QD layers the lifetime increases with increasing wavelength, clearly indicating the significant vertical electronic coupling between QDs.
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73.63.Kv Quantum dots
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
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